Abstract

Using individual patient data from 10 industry-sponsored randomized, controlled trials of rhBMP-2 including 1,255 patients, linear and generalized linear mixed models were used to assess effects of patient characteristics on estimates of effectiveness and harms of rhBMP-2.

Results

At 6 months, patients younger than 60 years had higher odds of fusion with rhBMP-2 versus ICBG (OR: 3.17, 95% CI: 1.20 to 8.37), but there was no treatment difference in persons over 60 years (OR: 1.12, 95% CI: 0.37 to 3.37). At 24 months, smokers had significantly higher odds of fusion with rhBMP-2 versus ICBG (OR: 4.90, 95% CI: 2.42 to 9.91), but there was no treatment difference in non-smokers (OR: 1.45, 95% CI: 0.85 to 2.47). In normal and overweight patients, rhBMP-2 was associated with higher odds of fusion versus ICBG at 24 months (Normal weight OR: 3.14, 95% CI: 1.46 to 6.73; Overweight OR: 2.60, 95% CI 1.29 to 5.22). For obese patients, effects of rhBMP-2 were smaller and not statistically significant (OR: 1.92, 95% CI: 0.82 to 4.50), and for severely obese patients, there was a non-significant trend for decreased odds of fusion in rhBMP-2 versus ICBG (OR: 0.36, 95% CI: 0.11 to 1.11). Similar results were found for the outcome of success, with normal weight patients having significantly higher odds of success with rhBMP-2 versus ICBG at 24 months (OR: 2.17, 95% CI: 1.36 to 3.44), but no treatment difference for all other weight groups.

Patients without a previous back surgery had reduced odds for related or related, severe adverse events at 24 months with rhBMP-2 as opposed to ICBG (related OR: 0.22, 95% CI: 0.09 to 0.51; related, severe OR: 0.09 95% CI: 0.03 to 0.32). For patients with a previous back surgery, there was not a significant treatment difference in harms (related OR: 2.10, 95% CI: 0.86 to 5.09; related, severe OR: 1.41, 95% CI: 0.53 to 3.77).

Limitations

Analyses are limited by the data in that there was up to 12% missing data on outcomes at 24 months and patients and study staff was not blinded to the treatment.

Conclusions

The results indicate that baseline smoking status, age, BMI and presence of a previous surgery had an impact on estimates of effectiveness and harms for rhBMP-2 versus ICBG in lumbar spinal fusion. There is preliminary support for rhBMP-2 increasing fusion for smokers and individuals under the age of 60, and improving fusion and success for patients of normal weight, but not for patients that are obese or severely obese, where rhBMP-2 may be less effective than ICBG. Also, rhBMP-2 resulted in decreased device-related adverse events in individuals with no previous back surgeries but not within individuals with a previous back surgery. Future studies of rhBMP-2 should include planned subgroup analysis in patients over 60, smokers, patients that are obese and severely obese, and individuals with previous back surgeries.

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